Generally, an AlGaInN, which is a gallium nitride based compound semiconductor including a small amount of an indium added thereto, is widely used for an active layer of a blue laser diode or a blue LED (light emitting diode).
A 2-step MOVPE (metal organic vapor phase epitaxy) is a general method for controlling a growth of an AlGaInN crystal. In accordance with the method, the AlGaInN crystal is grown to a thickness of tens of nanometer (nm) on a sapphire substrate at a low temperature ranging approximately from 400 to 900° C., and the AlGaInN crystal is further grown at a high temperature of approximately 1,050° C.
When an AlGaInN buffer layer is formed on a sapphire wafer at the low temperature, a planar thin film having a polycrystalline characteristic is formed. When the temperature is raised and the thin film is subjected to an optimal heat treatment at the high temperature, a column of the AlGaInN crystal is formed. The AlGaInN crystal grows in a lateral direction in a planar fashion at the high temperature based on the AlGaInN crystal. After the AlGaInN crystal is grown to a certain thickness, the AlGaInN crystal of a single crystal having a relatively smooth surface is obtained. A condition of the heat treatment of the buffer layer is dependant upon the growth of the buffer layer and the thickness thereof.
However, the process for forming the buffer layer is carried out within a MOCVD (metal organic chemical vapor deposition) process such that a time required to carry out the MOCVD process is prolonged. Particularly, as the time to carry out the MOCVD process is prolonged, a run time of a MOCVD reactor necessary for fabricating a device is significantly prolonged. In addition, the buffer layer during the grown thereof cannot be estimated and a throughput of the MOCVD process is reduced.